Volatile anaesthetics relax airway smooth muscle in vitro. The amount of relaxation might depend on the type and concentration of volatile anaesthetics, the calibre and precontraction level of the bronchi, and also on the species considered. These effects were investigated on isolated human bronchi.Isometric relaxations produced by halothane, isoflurane and desflurane bubbled on human bronchial rings precontracted with carbachol were recorded and compared with time controls.Volatile anaesthetics induced a concentration-dependent relaxation at 0.66, 1.33 and 2 minimum alveolar concentration (MAC). The relaxation was greater in mildly (carbachol 3610 -7 M) than in highly (carbachol 2610 -6 M) precontracted bronchi. Halothane was more potent in relaxing distal as compared to proximal bronchi; this differential effect was less pronounced with isoflurane and not observed with desflurane. While the three volatile anaesthetics induced similar relaxation on proximal bronchi, halothane was significantly more potent than desflurane on distal bronchi, with isoflurane being intermediate. The relaxation induced by 1.33 MAC of halothane, isoflurane and desflurane on moderately precontracted distal bronchi (carbachol 1610 -6 M) was attenuated by pretreatment with glibenclamide 1610 -5 M. In conclusion, halothane, isoflurane and desflurane exert direct but differential relaxant effects on human isolated bronchial smooth muscle. This may provide supplemental bronchodilation during anaesthesia. Although adenosine triphosphatesensitive K z channels are involved in these relaxant effects, they are unlikely to explain the observed differences between the three volatile anaesthetics. Eur Respir J 2002; 20: 286-292. Halothane and isoflurane are well-established bronchodilators in vivo both in animals [1][2][3][4][5] and humans [6,7]. Part of this bronchodilation is due to a direct effect on airway smooth muscle. For example, in dogs in vivo, the direct relaxant effect of halothane on airway smooth muscle contributed as much as the indirect effect on the vagal pathway [4]. These direct relaxant effects in vivo have been reproduced in vitro in many animal studies [8][9][10][11][12][13][14][15][16][17][18][19]. However, the intensity of the relaxation in vitro varies widely among studies. Factors that may explain these variations include: 1) anaesthetic concentration; 2) level of precontraction and contractile agonist used [11]; 3) airway calibre [13,19,20]; 4) differences in efficacy between volatile anaesthetics [7,13,17,20]; and 5) animal species. This latter factor might be particularly important, and so far, no in vitro studies involving volatile anaesthetics appear to be available on human airway smooth muscle.Desflurane, a more recent volatile anaesthetic, has some interesting properties including rapid onset/ offset of action. However, breath-holding, partial laryngospasm and coughing have been reported during induction of anaesthesia with desflurane in humans [21]. Such irritant effects on the upper airways do not seem...